fix: string reading

Author: andrewmd5

src/abi.ts

@@ -122,9 +122,11 @@ export class WASIAbi {
   ];
 
   private encoder: TextEncoder;
+  private decoder: TextDecoder;
 
   constructor() {
     this.encoder = new TextEncoder();
+    this.decoder = new TextDecoder();
   }
 
   writeString(memory: DataView, value: string, offset: number): number {
@@ -133,6 +135,12 @@ export class WASIAbi {
     buffer.set(bytes);
     return bytes.length;
   }
+
+  readString(memory: DataView, ptr: number, len: number): string {
+    const buffer = new Uint8Array(memory.buffer, ptr, len);
+    return this.decoder.decode(buffer);
+  }
+  
   byteLength(value: string): number {
     return this.encoder.encode(value).length;
   }

src/features/fd.ts

@@ -814,17 +814,15 @@ export function useMemoryFS(
         opened_fd: number
       ) => {
         const view = memoryView();
-        let path = "";
-        for (let i = 0; i < pathLen; i++) {
-          path += String.fromCharCode(view.getUint8(pathPtr + i));
-        }
 
         if (dirfd < 3) return WASIAbi.WASI_ERRNO_NOTDIR;
 
         const dirEntry = getFileFromFD(dirfd);
         if (!dirEntry || dirEntry.node.type !== "dir")
           return WASIAbi.WASI_ERRNO_NOTDIR;
 
+        const path = abi.readString(view, pathPtr, pathLen);
+
         const guestPath =
           (dirEntry.path.endsWith("/") ? dirEntry.path : dirEntry.path + "/") +
           path;
@@ -876,17 +874,15 @@ export function useMemoryFS(
         opened_fd: number
       ) => {
         const view = memoryView();
-        let path = "";
-        for (let i = 0; i < pathLen; i++) {
-          path += String.fromCharCode(view.getUint8(pathPtr + i));
-        }
 
         if (dirfd < 3) return WASIAbi.WASI_ERRNO_NOTDIR;
 
         const dirEntry = getFileFromFD(dirfd);
         if (!dirEntry || dirEntry.node.type !== "dir")
           return WASIAbi.WASI_ERRNO_NOTDIR;
 
+        const path = abi.readString(view, pathPtr, pathLen);
+
         const guestPath =
           (dirEntry.path.endsWith("/") ? dirEntry.path : dirEntry.path + "/") +
           path;
@@ -938,19 +934,15 @@ export function useMemoryFS(
       ) => {
         const view = memoryView();
 
-        // Read the relative path from WASM memory.
-        let guestRelPath = "";
-        for (let i = 0; i < pathLen; i++) {
-          guestRelPath += String.fromCharCode(view.getUint8(pathPtr + i));
-        }
-
         // Get the base FD entry; it must be a directory.
         const file = getFileFromFD(fd);
         if (!file) return WASIAbi.WASI_ERRNO_BADF;
         if (file.node.type !== "dir") {
           return WASIAbi.WASI_ERRNO_NOTDIR;
         }
 
+        const guestRelPath = abi.readString(view, pathPtr, pathLen);
+
         // Compute the full guest path.
         const basePath = file.path;
         const fullGuestPath = basePath.endsWith("/")